Directions in High Energy Physics

1
Directions in High Energy Physics

• UCSB Physics Department Retreat
• September 20, 2000
• Jeffrey D. Richman
• for the Experimental HEP Group

2
Outline

• Big questions/overview
• perspective
• big questions
• UCSB HEP group
• people
• projects
• Prospects and conclusions

3
Particle physics in perspective

• We are entering a new era
• Most objects so far studied have masses in the
  range
• 0 lt M lt 10 GeV
• u, d, s, c, b (quarks) e, m, t (charged
  leptons) ne, nm, nt (neutrinos) g, gluons
  (gauge bosons)
• Important exceptions!
• M(W) 80.4 GeV M(Z) 91.2 GeV
  M(t) 174 GeV
• These heavy particles are indicative of a new
  mass scale that we are just beginning to explore
• 0.1 TeV - 2 TeV
• Another mass frontier very light neutrinos. Tiny
  differences in Mn2 accessible via oscillations!
  Super-K has strong evidence for nm disappearance.

4
An experimental perspective

• ee- storage rings (recirculating beams stored
  1-2 hours)
• CESR (10 GeVgtbbar) -- PEP-II,
  KEKB (10 GeV, 2 rings, multibunch op)
• LEP/LEP2 (91-gt208 GeV Z physics, WW-
  production)
• ee- linear colliders (need to reduce
  synchrotron rad., single pass collisions, tiny
  beam cross sections, polarized beams)
• SLC (91 GeVgt Z physics)
• NLC, JLC, TESLA (all under consideration) (gt500
  GeV)
• hadron colliders (discovery machines ?)
• p pbar FNAL Tevatron facilities for pbar
  production and cooling (2 TeV start 4/01)
• pp LHC at CERN (strong US participation)
  (14 TeV)
• neutrino sources
• p decay nm new US experiments MINOS (760
  km), MiniBooNE (short baseline)
• atmospheric, solar (Super-K,SNO,)
• muon storage ring (50 GeV m beam under
  consideration) get nm and ne
• special underground labs-dark matter, proton decay

5
BaBar/PEP-II at SLAC
PEP-II highest luminosity storage ring in the
world. -asymmetric energies -multibunch operation
6
TeV Scale Physics CDF (Fermilab)
7
Big Questions
8
Big questions

• What is the origin of electroweak symmetry
  breaking? What sets the values of particle
  masses?
• Are there supersymmetric partners to the
  particles? Are there SUSY partners with masses
  below the 1 TeV scale?
• Can matter-antimatter asymmetries (CP violation)
  be explained within the framework of the SM? Is
  new physics required? What explains the
  matter-antimatter asymmetry of the universe?
• What is the pattern and origin of neutrino masses
  and mixings?
• Are there sterile neutrinos?
• Is there CP violation in neutrino interactions?
• What makes up non-baryonic dark matter ( weakly
  interacting massive particles?)
• Are quarks and leptons composite particles?

9
more big questions

• Are there additional, very heavy gauge bosons?
• Are there observable extra dimensions? Is there
  gravitational radiation in high-energy
  collisions?
• Why is CP violation absent in the strong
  interactions?
• What is the lifetime of the proton?

These questions, when translated into an actual
research program, typically expand by a factor of
10-100.
10
Electroweak Symmetry Breaking

• What is the mechanism that gives weak gauge
  bosons (W, Z) masses of order 100 GeV, while
  leaving the photon massless?
• EW interactions in the SM are based on SU(2)XU(1)
  gauge symmetry, which all mass terms violate.
  Masses can appear because new interactions cause
  this symmetry to be spontaneously broken.
• What is the nature of the Higgs sector? Is SUSY
  involved?
• Minimal model single Higgs boson (scalar), but
  actual sector could well be much more complex.
• How many Higgs bosons are there? Is the Higgs
  composite?
• Do Higgs bosons couple to fermions in the
  expected pattern?

11
Supersymmetry

• Supersymmetry protects the masses of scalar
  particles (Higgs) from enormous loop corrections
  without the fine tuning of parameters (solving
  the hierarchy problem). Divergences are
  cancelled by presence of both fermions and bosons
  in loops.
• SUSY doubles the number of particles and leads to
  a complex phenomenology
• Spin 1/2 particles in the SM have spin 0
  super-partners
• Spin 1 particles in the SM have spin1/2
  super-partners
• SUSY must be broken (superpartners have not been
  observed). The Higgs mass scale becomes
  proportional to SUSY mass scale rather than
  Planck scale.

12
An experimental SUSY program

• Is it really SUSY?
• New particle quantum numbers, spin, statistics
• identication of complete SU(2)XU(1) multiplets
• SUSY relation of coupling constants
• Major spectrum parameters
• gaugino/Higgsino mixing
• gaugino mass ratios m1 m2 m3
• flavor universality of q, lR, lL masses?
• QlRlL mass ratios
• signatures of gauge- or anomaly-mediation
• signatures of R-parity violation
• Third generation and EWSB
• determination of m, tanb
• mixing of L/R partners for t, b, t
• h0 mass
• H0, A0, H masses and branching ratios
• Precision effects...

(From M. Peskin, Physics Goals of a Linear
Collider)
13
(No Transcript)
14
HEP group where are we now?

• We already had to examine our future--one year
  ago! Strong and clear group consensus on what we
  needed to do.
• Exploration of the TeV energy scale is the next
  major goal of HEP. Enormous potential for major
  discoveries.
• Successful senior-level hire Joseph Incandela
  from Fermilab. Joe is a leader on two major
  experiments at the energy frontier, CDF and CMS.
• Our technological expertise in high-precision
  silicon tracking systems is highly relevant to
  LHC physics!
• Large number of tracksgt need fine segmentation
  
• b-quarks may be important in Higgs/SUSY processes

15
HEP group where are we now?

• The group now has 4 faculty (Campagnari,
  Incandela, Nelson, and Richman)
• The group includes about 27 people total,
  including students, postdocs, staff physicists,
  engineers, and technicians.
• A junior-level search is approved for this fall
  we should have no problem attracting top-quality
  person. Priority is to strengthen the TeV physics
  effort.
• We had very good support from UCSB on the
  Incandela search.

16
HEP Group current program
17
Matter-Antimatter Asymmetry

• Can CP violation be explained within the
  framework of the standard model, or are these
  effects due to new physics?
• Some CP asymmetries in the B-meson system are
  expected to be of order unity in the SM! (Compare
  to 10-3 in kaon system.)
• This year race between BaBar and Belle (Japan)
  to obtain first sensitive CP asymmetry
  measurements in B system. In reality, these are
  long-term programs.

18
CP Violation in the B meson system
Amplitudes can carry weak (CP violating) phases
from the CKM matrix in the SM or from new
physics. Such phases change the sign of the
interference for particle and antiparticle decays.
19
BaBar Silicon Vertex Tracker
20
BaBar/PEP-II Data Taking
21
BaBar Event Display (fisheye view)
22
Cryogenic Dark Matter Search (CDMS)

• CDMS-I pilot experiment in Stanford Underground
  Facility
• CDMS-II now under construction to be installed
  in Soudan mine
• Detectors from LBNL and Stanford UCSB is
  providing DAQ system, passive and active veto
  shields.

23
Expectations from CDMS-II
24
TeV Scale Physics at the LHC
25
How do experiments happen?

• Many particle experiments today are capable of a
  very broad range of physics studies.
• In this sense they are like observatories, but
  the initial conditions are controlled.
• However, HEP experiments are built by their
  users, who also calibrate, maintain, and operate
  the detectors.
• The UCSB group is unusual in maintaining the
  ability to construct sophisticated detectors.
• It takes 2-3 years to fully understand a new
  detector. Some physics results can be produced in
  the first year others require a much more
  refined understanding of the detector..
• Although the collaborations are becoming very
  large, most physics results are produced by
  groups of 3-10 people.

26
Comments

• The department must be strong in all of our
  research areas.
• Many groups are near critical mass relatively
  small downward fluctuations can create major
  problems.
• Growth of the Physics Dept from 30 to about 40
  should have many benefits, including an even
  better departmental reputation.

27
Conclusions/Prospects

• The Incandela hire is almost optimally matched to
  our goals
• the new experiments at TeV scale diversify our
  program and address the driving questions of HEP
• the required hardware expertise is well matched
  to our group
• we will establish very high profile efforts right
  from the start
• The main area in which we have no effort is
  neutrino physics.
• This is clearly an exciting and rapidly
  developing area.
• However, we have just added two new experiments
  to our group, and we believe that our first
  priority should be to strengthen these new
  efforts.